Use the HTTP Last-Modified http header as the mtime value for ADD cmd when present

Closes #8331

Signed-off-by: Doug Davis <dug@us.ibm.com>

builder/internals.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net/http"
 	"net/url"
 	"os"
 	"path"
@@ -254,8 +255,21 @@ func calcCopyInfo(b *Builder, cmdName string, cInfos *[]*copyInfo, origPath stri
 		fmt.Fprintf(b.OutStream, "\n")
 		tmpFile.Close()
 
-		// Remove the mtime of the newly created tmp file
-		if err := system.UtimesNano(tmpFileName, make([]syscall.Timespec, 2)); err != nil {
+		// Set the mtime to the Last-Modified header value if present
+		// Otherwise just remove atime and mtime
+		times := make([]syscall.Timespec, 2)
+
+		lastMod := resp.Header.Get("Last-Modified")
+		if lastMod != "" {
+			mTime, err := http.ParseTime(lastMod)
+			// If we can't parse it then just let it default to 'zero'
+			// otherwise use the parsed time value
+			if err == nil {
+				times[1] = syscall.NsecToTimespec(mTime.UnixNano())
+			}
+		}
+
+		if err := system.UtimesNano(tmpFileName, times); err != nil {
 			return err
 		}
 

docs/sources/reference/builder.md

@@ -376,7 +376,11 @@ destination container.
 All new files and directories are created with a UID and GID of 0.
 
 In the case where `<src>` is a remote file URL, the destination will
-have permissions of 600.
+have permissions of 600. If the remote file being retrieved has an HTTP
+`Last-Modified` header, the timestamp from that header will be used
+to set the `mtime` on the destination file. Then, like any other file
+processed during an `ADD`, `mtime` will be included in the determination
+of whether or not the file has changed and the cache should be updated.
 
 > **Note**:
 > If you build by passing a `Dockerfile` through STDIN (`docker

integration-cli/docker_cli_build_test.go

@@ -7,9 +7,11 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"regexp"
 	"strings"
+	"syscall"
 	"testing"
 	"time"
 
@@ -2214,6 +2216,64 @@ func TestBuildADDRemoteFileWithoutCache(t *testing.T) {
 	logDone("build - add remote file without cache")
 }
 
+func TestBuildADDRemoteFileMTime(t *testing.T) {
+	name := "testbuildaddremotefilemtime"
+	defer deleteImages(name)
+
+	server, err := fakeStorage(map[string]string{"baz": "hello"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer server.Close()
+
+	ctx, err := fakeContext(fmt.Sprintf(`FROM scratch
+        MAINTAINER dockerio
+        ADD %s/baz /usr/lib/baz/quux`, server.URL), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ctx.Close()
+
+	id1, err := buildImageFromContext(name, ctx, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	id2, err := buildImageFromContext(name, ctx, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id1 != id2 {
+		t.Fatal("The cache should have been used but wasn't - #1")
+	}
+
+	// Now set baz's times to anything else and redo the build
+	// This time the cache should not be used
+	bazPath := path.Join(server.FakeContext.Dir, "baz")
+	err = syscall.UtimesNano(bazPath, make([]syscall.Timespec, 2))
+	if err != nil {
+		t.Fatalf("Error setting mtime on %q: %v", bazPath, err)
+	}
+
+	id3, err := buildImageFromContext(name, ctx, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id1 == id3 {
+		t.Fatal("The cache should not have been used but was")
+	}
+
+	// And for good measure do it again and make sure cache is used this time
+	id4, err := buildImageFromContext(name, ctx, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id3 != id4 {
+		t.Fatal("The cache should have been used but wasn't - #2")
+	}
+	logDone("build - add remote file testing mtime")
+}
+
 func TestBuildADDLocalAndRemoteFilesWithCache(t *testing.T) {
 	name := "testbuildaddlocalandremotefilewithcache"
 	defer deleteImages(name)